A/C Blower on 92 500SEL

[wmkoles@msn.com]

My Heat/AC blower only operates at idle with heavy elec load. Doesn't work until I put in drive at stop and turn on rear defrost and heated seats....then runs fine until I accelerate or put in park, then dies. Motor runs fine at variable speeds so I think it's the controller????? Any other possibilities before I lay out the $250++
Also, how do I access motor and controller on the 140 chassis????

Can't stay cool and move too....HELP!!!!!!!!